The effect of proton irradiation on magnetic properties of lithium ferrites

The effect of proton irradiation on magnetic properties of lithium ferrites has been investigated with x-ray diffraction (XRD), magnetization, and Mossbauer spectroscopy measurements. Li0.5Fe2.5O4 powders have been fabricated by the sol-gel method. Following the annealing at 700 degrees C, these samples have been proton irradiated with 1, 5, and 10 pC/mu m(2). The analysis of XRD patterns by Rietveld refinement method shows that these samples have ordered cubic spinel structures with space group of P4(3)32. We have observed that the corresponding lattice constant a(0) linearly increases from 8.3301 to 8.3314 +/- 0.0001 angstrom with increasing proton irradiation. Compared to nonirradiated sample, which has the saturation magnetization (M-s) of 66.4 emu/g and oxygen occupancy of 3.9980 at room temperature, the values of magnetization and oxygen occupancy at room temperature are 66.0, 62.6, and 60.8 emu/g and 3.9840, 3.9452, and 3.9272, respectively, for 1, 5, and 10 pC/mu m(2) irradiated powders. Also, the coercivity (H-c) decreases from 175.6 to 154.0 Oe with increasing proton irradiation. The Mossbauer spectra taken at room temperature show that the values of isomer shift (delta) for the tetrahedral (A) and octahedral (B) sites are consistent with the Fe3+ valence state. The results suggest that the proton irradiation induces the oxygen vacancy defects, which in turn leads to the changes in magnetic properties. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3070611]